The radioimmunodetection of tumors has been successfully accomplished in several animal experimental studies and to a limited degree in humans, using 131 I labeled IgG antibodies. However, since 131 I is not ideal radionuclide for scintigraphic use, we have investigated and developed new methods for the labeling of immunoreactive immunoglobulins with 99 mTc and 111 I in. These radionuclides have a number of physical advantages over 131 I for external imaging. We have chosen alpha fetoprotein (AFP) secreting tumors as a model system to evaluate the effectiveness of these new radionuclide labeling techniques to localize AFP secreting tumors in vivo. AFP is a fetal specific protein, resynthesized by malignant liver and germ cell tumors. In contrast to Carcinoembryonic Antigen (CEA) and other putative tumor associated antigens, AFP is not normal adult tissue. Therefore, it is an ideal model system to evaluate the effectiveness of new radioimmunodetection methods. We plan to study the biodistribution and clearance of technetium and indium labeled F(ab')2 anti AFP antibodies in a nude mouse model bearing a human AFP producing tumor; to determine the ability of technetium and indium labeled F(ab')2 antibody to localize AFP producing liver and germ cell tumors in patients using external scanning; to explore and develop new methods of utilizing photon emission tomography to enhance localization of specific labeled antibodies in vivo; to produce and label high affinity monoclonal hybridoma anti AFP antibodies to compare its localization capacity to labeled heterologous antibody. These studies, using innovative and improved methodology for labeling and localizing antitumor antibodies, should provide a useful model for localizing antibodies to other tumor associated antigens.